Improvement of a method for chain-length distribution analysis of wheat amylopectin

Application of co-precipitated glutinous rice starch as a multifunctional excipient in direct compression tablets

Two key properties of excipients for inclusion in direct compression tablets are flowability and compactibility. Glutinous rice starch (GRS) has poor flowability, which limits its use in direct compression tablets. This study aimed to create a multifunctional direct compression excipient (filler binder disintegrant) with improved flowability from GRS by the co-precipitation method. The physicochemical and pharmaceutical properties of the co-precipitated GRS (cpGRS) were investigated. The optimum conditions for producing cpGRS (0.43 M sodium hydroxide solution, 7.09% PVP K30, 14.02% calcium carbonate, 95 min of mixing time and pH of 6.97) resulted in 68.80% yield, fair to good flowability, acceptable tablet strength, and fast disintegration. The FT-IR spectra of cpGRS showed no significant shifts in the key peaks, which indicates that there was an absence of chemical interactions within cpGRS. X-ray diffractograms also showed no significant changes, indicating that the GRS granules, calcium carbonate, and PVP K30 components remained unaltered during co-precipitation. cpGRS also demonstrated a dilution capacity of 50% when paracetamol was used as model drug. When cpGRS was combined with domperidone or propranolol hydrochloride it showed a better deformation capability than the physical mixtures. Although cpGRS was sensitive to lubricant, the hardness and tensile strength were higher than common strength for general purpose use in tablets. When compared to the physical mixture, pregelatinized starch and directly compressible calcium carbonate, the results showed that cpGRS tablets of both model drugs passed the friability test, demonstrated the best disintegration property, provided the fastest and highest drug release profile for propranolol, and improved the drug release profile for domperidone. For propranolol-cpGRS tablets, dissolution medium at different pH did not affect the dissolution profile. For domperidone-cpGRS tablets, the pH of dissolution medium did affect the dissolution profile of the tablets. This was according to the API solubility. These results reveal that cpGRS is an excellent multifunctional i.e., filler, binder, and disintegrant excipient suitable for direct compression tablets. The main component is natural. The preparation method is simple, quick, and efficient. This method does not produce harmful waste and requires only basic equipment, and affordable reactants and devices.

A novel rice dull gene, LowAC1, encodes an RNA recognition motif protein affecting Waxyb pre-mRNA splicing

A new dull grain rice mutant with low amylose content, designated lowac1, has been isolated and characterized. To identify the causal mutation site, resequencing of the whole genome and analysis of a cleaved amplified polymorphic sequence (CAPS) marker were performed. Genotypes using the CAPS marker of the identified LowAC1 gene encoding an RNA recognition motif (RRM) protein were entirely consistent with low amylose phenotypes in BC₁F₂ progeny. Moreover, the segregation of BC₁F₂ population indicated that the low amylose phenotype was controlled by a single recessive gene. lowac1 involves a single-nucleotide polymorphism from G to A within the gene, resulting in the stop codon generation. The RRM protein deletion in the mutant seed specifically affected the splicing efficiency of Waxy^b (Wx^b) in the 5' splice site of intron 1, resulting in decreased protein levels of granule-bound starch synthase I (GBSSI) encoded by Wx^b. Whereas, the RRM protein did not affect amylose content in Wx^a of indica variety. Also, the mutation induced a little variation in the expression levels of some genes involved in starch biosynthesis. Particularly, expression levels of SBEIIb, PUL, and AGPL2 mRNAs in lowac1 mutant were approximately two times higher compared to the corresponding wild type (WT) genes. Aside from low amylose content, lowac1 seeds included an amylopectin structure reducing short chains compared to that of WT seeds. Overall, our data suggest that LowAC1 is a novel regulatory factor for starch synthesis in rice.

Transactivation of Sus1 and Sus2 by Opaque2 is an essential supplement to sucrose synthase-mediated endosperm filling in maize

The endosperm-specific transcription factor Opaque2 (O2) acts as a central regulator for endosperm filling, but its functions have not been fully defined. Regular o2 mutants exhibit a non-vitreous phenotype, so we used its vitreous variety Quality Protein Maize to create EMS-mutagenesis mutants for screening o2 enhancers (oen). A mutant (oen1) restored non-vitreousness and produced a large cavity in the seed due to severely depleted endosperm filling. When oen1 was introgressed into inbred W64A with a normal O2 gene, the seeds appeared vitreous but had a shrunken crown. oen1 was determined to encode Shrunken1 (Sh1), a sucrose synthase (SUS, EC 2.4.1.13). Maize contains three SUS-encoding genes (Sh1, Sus1, and Sus2) with Sh1 contributing predominantly to the endosperm. We determined SUS activity and found a major and minor reduction in oen1 and o2, respectively. In o2;oen1-1, SUS activity was further decreased. We found all Sus gene promoters contain at least one O2 binding element that can be specifically recognized and be transactivated by O2. Sus1 and Sus2 promoters had a much stronger O2 transactivation than Sh1, consistent with their transcript reduction in o2 endosperm. Although sus1 and sus2 alone or in combination had no perceptible phenotype, either of them could dramatically enhance seed opacity and cavity in sh1, indicating that transactivation of Sus1 and Sus2 by O2 supplements SUS-mediated endosperm filling in maize. Our findings demonstrate that O2 transcriptionally regulates the metabolic source entry for protein and starch synthesis during endosperm filling.

High temperature inhibits the accumulation of storage materials by inducing alternative splicing of OsbZIP58 during filling stage in rice

High temperature (HT) has an adverse effect on rice grain filling by inhibiting the accumulation of storage materials. However, the regulatory mechanism of this inhibition remains unknown. Here, we report that Opaque2 like transcription factor OsbZIP58 is a key factor regulating storage material accumulation under HT. The OsbZIP58 gene promotes expression of many seed storage protein genes and starch synthesis genes while inhibits expression of some starch hydrolyzing α-amylase genes under HT. The loss of OsbZIP58 function leads to floury and shrunken endosperms and dramatically reduced storage materials in the seeds under HT. HT is found to affect alternative splicing of OsbZIP58, promoting the formation of the truncated OsbZIP58β protein form over the full-length OsbZIP58α protein form. The OsbZIP58β form has a lower transcriptional activity than the OsbZIP58α form, especially under HT condition. Interestingly, rice varieties with less heat sensitivity have reduced alternative splicing of OsbZIP58. Therefore, OsbZIP58 is a crucial gene in regulating storage material accumulation under HT and lower alternative splicing of OsbZIP58 may contribute to heat tolerance during grain filling.

Influence of anionic, neutral, and cationic polysaccharides on the in vitro digestibility of raw and gelatinized potato starch

BACKGROUND

Polysaccharides have been expected to have a suppressive effect on starch digestibility by blending. The objective of this study was to investigate the effects of anionic (xanthan gum), neutral (guar gum), and cationic (chitosan) polysaccharides on the in vitro digestibility of raw and gelatinized starch using six potato cultivars differing in phosphorus content.

RESULTS

By comparing the starch digestibility between potato cultivars, a significant difference was observed for the raw starches, and 'Benimaru', which is a potato cultivar containing a higher proportion of short-chain amylopectin and the lowest phosphorus content in starch, showed a distinctly faster rate of starch hydrolysis. The added polysaccharides decreased the extent of digestion of both raw and gelatinized starches. No significant correlation between phosphorus content and the extent of starch digestion was observed in mixed systems, whereas significant correlations were noted between the extent of starch digestion and Rapid Visco Analyser parameters. The extent of raw and gelatinized starch digestion negatively correlated with pasting temperature, initial viscosity before heating, and peak viscosity (P < 0.01).

CONCLUSION

The added polysaccharides were observed to decrease the starch digestibility, and their suppressive effects were mainly dependent on the increase of viscosity rather than chemical interactions. A combination of potato cultivar and type of polysaccharide was proved to be important for nutritional value of potato starch. © 2020 Society of Chemical Industry.

Comparison of textural properties and structure of gels prepared from cooked rice grain under different conditions

The objective of this study was to investigate the effects of rice variety, water content, and preparation temperature on the textural properties of gels processed from cooked rice grains via high-speed shear homogenization. Rice gels were prepared from seven high-amylose rice varieties. The results demonstrated the significant differences in rice gel hardness and hardening rates during storage based on the rice variety used. The proportion of short chains of amylopectin was negatively correlated with the hardness of the rice gel. The sample temperature before shear treatment also influenced the rice gel hardness. Rice gels prepared from cooked rice maintained at 75°C prior to homogenization showed a higher breaking force than those from cooked rice at 25°C. Observation using scanning electron microscopy demonstrated the tendency of the cooked rice sample maintained at 75°C to form a finer gel network after homogenization than those at 25°C from the same rice variety.

qAC2, a novel QTL that interacts with Wx and controls the low amylose content in rice (Oryza sativa L.)

This manuscript reports the fine mapping of a novel QTL, qAC2 controlling the low amylose in rice. The action mechanism of the qAC2 is also investigated by the analysis of genetic interactions to Wx (a), Wx (b), du1, du2 and du3. Amylose content of the rice (Oryza sativa L.) endosperm greatly affects starch properties and eating quality of cooked rice. Seeds of japonica rice cultivar Kuiku162 have low amylose content (AC) and good eating quality. Our analysis revealed a novel QTL, designated as qAC2 that contributed to the low AC of Kuiku162. qAC2 was fine mapped within a 74.9-kb region between two insertion and deletion markers, KID3001 and KID5101, on the long arm of chromosome 2. Seven genes are predicted in this region, but none of them is known to be related to the regulation of AC. The AC of a near-isogenic line (NIL110) carrying qAC2 (Kuiku), the Kuiku162 allele of qAC2, in the genetic background of japonica cultivar Itadaki was lower by 1.1% points than that of Itadaki. The chain length distributions of amylopectin were similar in NIL110 and Itadaki; therefore, the low AC of NIL110 was caused by a decrease in the actual AC, but not by a difference in the amylopectin structure. The interaction analyses revealed that qAC2 (Kuiku) has epistatic interaction with Wx (a). The qAC2 (Kuiku) has epistatic interactions with two loci, du1 and du2, on Wx (b), whereas the genetic effect of qAC2 (Kuiku) has additive to that of du3 on Wx (b). Thus, similar to du1 and du2, qAC2 may have a function related to Wx (b) mRNA splicing.

Development of formulae for estimating amylose content, amylopectin chain length distribution, and resistant starch content based on the iodine absorption curve of rice starch

Not only amylose but also amylopectin greatly affects the gelatinization properties of rice starch and the quality of cooked rice grains. We here characterized the starches of 32 rice cultivars and evaluated the relationship between their iodine absorption curve, apparent amylose content (AAC), pasting property, resistant starch (RS) content, and chain length distribution of amylopectin. We found that the iodine absorption curve differed among the various sample rice cultivars. Using the wavelength at which absorbance becomes maximum on iodine staining of starch (λmax), we propose a novel index, "new λmax" (AAC/(λmax of sample rice starches-λmax of glutinous rice starch)). We developed the novel estimation formulae for AAC, RS contents, and amylopectin fractions with the use of λmax and "new λmax." These formulae would lead to the improved method for estimating starch properties using an easy and rapid iodine colorimetric method.

OsbZIP58, a basic leucine zipper transcription factor, regulates starch biosynthesis in rice endosperm

Starch composition and the amount in endosperm, both of which contribute dramatically to seed yield, cooking quality, and taste in cereals, are determined by a series of complex biochemical reactions. However, the mechanism regulating starch biosynthesis in cereal seeds is not well understood. This study showed that OsbZIP58, a bZIP transcription factor, is a key transcriptional regulator controlling starch synthesis in rice endosperm. OsbZIP58 was expressed mainly in endosperm during active starch synthesis. osbzip58 null mutants displayed abnormal seed morphology with altered starch accumulation in the white belly region and decreased amounts of total starch and amylose. Moreover, osbzip58 had a higher proportion of short chains and a lower proportion of intermediate chains of amylopectin. Furthermore, OsbZIP58 was shown to bind directly to the promoters of six starch-synthesizing genes, OsAGPL3, Wx, OsSSIIa, SBE1, OsBEIIb, and ISA2, and to regulate their expression. These findings indicate that OsbZIP58 functions as a key regulator of starch synthesis in rice seeds and provide new insights into seed quality control.

Coexpression analysis identifies Rice Starch Regulator1, a rice AP2/EREBP family transcription factor, as a novel rice starch biosynthesis regulator

Starch biosynthesis is important for plant development and is a critical factor in crop quality and nutrition. As a complex metabolic pathway, the regulation of starch biosynthesis is still poorly understood. We here present the identification of candidate regulators for starch biosynthesis by gene coexpression analysis in rice (Oryza sativa). Starch synthesis genes can be grouped into type I (in seeds; sink tissues) and type II (in vegetative tissues; source tissues), and 307 and 621 coexpressed genes are putatively involved in the regulation of starch biosynthesis in rice seeds and vegetative tissues, respectively. Among these genes, Rice Starch Regulator1 (RSR1), an APETALA2/ethylene-responsive element binding protein family transcription factor, was found to negatively regulate the expression of type I starch synthesis genes, and RSR1 deficiency results in the enhanced expression of starch synthesis genes in seeds. Seeds of the knockout mutant rsr1 consistently show the increased amylose content and altered fine structure of amylopectin and consequently form the round and loosely packed starch granules, resulting in decreased gelatinization temperature. In addition, rsr1 mutants have a larger seed size and increased seed mass and yield. In contrast, RSR1 overexpression suppresses the expression of starch synthesis genes, resulting in altered amylopectin structure and increased gelatinization temperature. Interestingly, a decreased proportion of A chains in rsr1 results in abnormal starch granules but reduced gelatinization temperature, whereas an increased proportion of A chains in RSR1-overexpressing plants leads to higher gelatinization temperatures, which is novel and different from previous reports, further indicating the complicated regulation of starch synthesis and determination of the physicochemical properties of starch. These results demonstrate the potential of coexpression analysis for studying rice starch biosynthesis and the regulation of a complex metabolic pathway and provide informative clues, including the characterization of RSR1, to facilitate the improvement of rice quality and nutrition.

Evaluation of amylopectin clusters and their interaction with nonionic surfactants

The interaction between polyoxyethylene (7 and 23) dodecyl ether (Unitol L-70 and L-230, respectively) and polyoxyethylene (9.5) nonylphenol ether (Renex 95) with amylopectin was studied employing the relative intensities of pyrene fluorescence emission bands 1 to 3, and excimer to monomer ratios. The pyrene concentration was very low (1mumol/L), and the probe was added to amylopectin solution by two different methods. These experimental conditions have given information about how amylopectin branch structure affects the molecular diffusion in aqueous solution. Amylopectin clusters are formed from the biopolymer outer branches. The cluster polarity is similar to ethylene glycol, confirmed by the Reichardt dye measurements. Inside the clusters, amylopectin-Unitol surfactant complexes can form with cac and cmc dependent on the biopolymer concentration. The micellar aggregation number of 60+/-5 was determined through pyrene steady-state fluorescence quenching experiments.

Soluble starch synthase I effects differences in amylopectin structure between indica and japonica rice varieties

The effect of soluble starch synthase I (SSI) on differences of amylopectin structure between the indica and japonica rice varieties was investigated. Native-PAGE/active staining analysis showed that the SSI activity of an indica rice variety, "Kasalath", was significantly lower than that of a japonica rice variety, "Nipponbare", and that the low activity in "Kasalath" was maintained during seed development. The result of northern blot analyses suggests that the low expression of SSI in "Kasalath" is controlled at the transcription levels of SSI mRNA. Chain length distribution of amylopectin in F3 endosperms derived from a cross between two varieties showed that not only SSIIa but also SSI regulated the population of short chains. These results indicate that the low activity of SSI gives rise to the decrease of short chains in amylopectin of indica rice varieties, suggesting that SSI effects the differences in physicochemical properties between two varieties.

A Rice Family 9 Glycoside Hydrolase Isozyme with Broad Substrate Specificity for Hemicelluloses in Type II Cell Walls

An auxin analog, 2,4-D, stimulates the activity of endo-1,4-beta-glucanase (EGase) in rice (Oryza sativa L.). The auxin-induced activity from three protein fractions was purified to homogeneity from primary root tissues (based on SDS-PAGE and isoelectric focusing after Coomassie brilliant blue staining). Amino acid sequencing indicated that the 20 N-terminal amino acid sequence of the three proteins was identical, suggesting that these proteins may be cognates of one EGase gene. An internal amino acid sequence of the the rice EGase (LVGGYYDAGDNVK) revealed that this enzyme belongs to glycosyl hydrolase family 9 (GHF9). The major isoform of this rice GHF9 [molecular weight based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS): 51,216, isoelectric point (pI): 5.5] specifically hydrolyzed 1,4-beta-glycosyl linkages of carboxymethyl (CM)-cellulose, phosphoric acid-swollen cellulose, 1,3-1,4-beta-glucan, arabinoxylan, xylan, glucomannan, cellooligosaccharides [with a degree of polymerization (DP) >3] and 1,4-beta-xylohexaose, indicating a broader substrate range compared with those of other characterized GHF9 enzymes or EGases from higher plants. Hydrolytic products of two major hemicellulosic polysaccharides in type II cell walls treated with the purified enzyme were profiled using high-performance anion exchange chromatography (HPAEC). The results suggested that endolytic attack by rice EGase is not restricted to either the cellulose-like domain of 1,3-1,4-beta-glucan or the unsubstituted 1,4-beta-xylosyl backbone of arabinoxylan, but results in the release of smaller oligosaccharides (DP <6) from graminaceous hemicelluloses. The comparatively broader substrate range of this EGase with respect to beta-1,4-glycan backbones (glucose and xylose) may partly reflect different roles of gramineous and non-gramineous GHF9 enzymes.

Fractionation of starch hydrolysates into dextrins with narrow molecular mass distribution and their detection by high-performance anion-exchange chromatography with pulsed amperometric detection

Low levels of high-molecular-mass dextrins in starch hydrolysates can be detected by high-performance anion-exchange chromatography with pulsed amperometric detection in spite of their low responses by dialysis of the starch hydrolysate and fractionation of the resulting adialysate with ethanol (final concentration 30-80% at 6 degrees C). In doing so, dextrin fractions with a relatively narrow molecular mass distribution were obtained.

Biochemical and genetic analysis of the effects of amylose-extender mutation in rice endosperm

Biochemical analysis of amylose-extender (ae) mutant of rice (Oryza sativa) revealed that the mutation in the gene for starch-branching enzyme IIb (BEIIb) specifically altered the structure of amylopectin in the endosperm by reducing short chains with degree of polymerization of 17 or less, with the greatest decrease in chains with degree of polymerization of 8 to 12. The extent of such change was correlated with the gelatinization properties of the starch granules, as determined in terms of solubility in urea solution. The ae mutation caused a dramatic reduction in the activity of BEIIb. The activity of soluble starch synthase I (SSI) in the ae mutant was significantly lower than in the wild type, suggesting that the mutation had a pleiotropic effect on the SSI activity. In contrast, the activities of BEI, BEIIa, ADP-Glc pyrophosphorylase, isoamylase, isoamylase, pullulanase, and Suc synthase were not affected by the mutation. Therefore, it is stressed that the function of BEIIb cannot be complemented by BEIIa and BEI. These results strongly suggest that BEIIb plays a specific role in the transfer of short chains, which might then be extended by SS to form the A and B(1) chains of amylopectin cluster in rice endosperm.

The starch-debranching enzymes isoamylase and pullulanase are both involved in amylopectin biosynthesis in rice endosperm

The activities of the two types of starch debranching enzymes, isoamylase and pullulanase, were greatly reduced in endosperms of allelic sugary-1 mutants of rice (Oryza sativa), with the decrease more pronounced for isoamylase than for pullulanase. However, the decrease in isoamylase activity was not related to the magnitude of the sugary phenotype (the proportion of the phytoglycogen region of the endosperm), as observed with pullulanase. In the moderately mutated line EM-5, the pullulanase activity was markedly lower in the phytoglycogen region than in the starch region, and isoamylase activity was extremely low or completely lost in the whole endosperm tissue. These results suggest that both debranching enzymes are involved in amylopectin biosynthesis in rice endosperm. We presume that isoamylase plays a predominant role in amylopectin synthesis, but pullulanase is also essential or can compensate for the role of isoamylase in the construction of the amylopectin multiple-cluster structure. It is highly possible that isoamylase was modified in some sugary-1 mutants such as EM-273 and EM-5, since it was present in significant and trace amounts, respectively, in these mutants but was apparently inactive. The results show that the Sugary-1 gene encodes the isoamylase gene of the rice genome.